1. Technical Field
The present disclosure is directed to devices, systems and methods for catalyzing chemical reactions. More particularly, the present disclosure is directed to devices, systems, and methods for catalyzing chemical reactions via the use of dedicated reactors and/or micro-chemical systems.
2. Background Art
In general, fuel cell systems (e.g., systems employing electrochemical combustion of hydrogen gas) promise high-power, high-efficiency systems for meeting future propulsion and energy needs. For example, by utilizing electrochemical combustion of hydrogen gas, these systems generally overcome Carnot-cycle efficiency losses inherent to conventional direct-combustion engines. However, efficient, portable, and robust conversion of fuels (e.g., liquid fuels, diesel fuels, logistics fuels, naval logistics fuels, etc.) to hydrogen for subsequent electrochemical conversion remains an important challenge to realizing next-generation fuel cell energy systems.
In general, micro-chemical systems have been demonstrated as a promising technology for chemical processing, typically offering improved heat and mass transport owing to reduced characteristic lengths in mini- or micro-channels, and typically resulting in enhanced control of reaction temperature and hot-spot formation. Such systems have already been investigated as tools for: i) organic synthesis (see, e.g., De Mas, N., A. Gunther, T. Kraus, M. A. Schmidt and K. F. Jensen, “Scaled-Out Multilayer Gas—Liquid Microreactor with Integrated Velocimetry Sensors,” Ind. Eng. Chem. Res., 44(24), 8997-9013 (2005); Haswell, S. J., R. J. Middleton, B. O'Sullivan, V. Skelton, P. Watts and P. Styring, “The Application of Micro Reactors to Synthetic Chemistry,” Chem. Commun., (5), 391-398 (2001); DeWitt, S. H., “Microreactors for Chemical Synthesis,” Curr. Opin. Chem. Biol., 3(3), 350-356 (1999)); ii) high-energy laser chemistry (see, e.g., Wilhite, B. A., C. Livermore, Y. Gong, A. Epstein and K. F. Jensen, “Design of a MEMS-Based Chemical Oxygen-Iodine Laser (COIL) System,” IEEE J. of Quantum. Electron., 40, 1041 (2004a); Hill, T., L. Velasquez-Garcia, B. Wilhite, A. Epstein, K. Jensen and C. Livermore, “A MEMS Singlet-Oxygen Generator,” Hilton Head 2006: A Solid State Sensor, Actuator and Microsystems Workshop (2006)); and iii) high-temperature fuel reforming (see, e.g., Wilhite, B. A., S. E. Weiss, J. Y. Ying, M. A. Schmidt and K. F. Jensen, “Demonstration of 23 wt % Ag—Pd Micromembrane Employing 8:1 LaNi0.95Co0.05O3/Al2O3 Catalyst for High-Purity Hydrogen Generation,” Advanced Materials, 18, 1701 (2006); Holladay, J. D., Y. Wang and E. Jones, “Review of Developments in Portable Hydrogen Production Using Microreactor Technology,” Chem. Rev., 104(10), 4767-4790 (2004)).
Enhanced heat and mass transport within mini- or micro-channels has fueled significant research towards developing heat-integrated micro-chemical systems. Mini- or micro-channel networks demonstrating simple distribution schemes to combine: (i) catalytic combustion with endothermic reforming (see, e.g., Arana, L. R., S. B. Schaevitz, A. J. Franz, M. A. Schmidt and K. F. Jensen, “A Microfabricated Suspended-Tube Chemical Reactor for Thermally Efficient Fuel Processing,” J. Microelectromech. Syst., 12(5), 600-612 (2003)); (ii) combustion and vaporization (see, e.g., Tonkovich, A. I. Y., D. M. Jimenez, J. L. Zilka, M. J. LaMont, Y. Wang, R. S. Wegeng, “Microchannel Chemical Reactors for Fuel Processing,” Proceedings of the 2nd International Conference on Microreaction Technology, AIChE, New York, 186-195 (1998)); and (iii) combustion, reforming and vaporization (see, e.g., Pan, L. and S. Wang, “Methanol Steam Reforming in a Compact Plate—Fin Reformer for Fuel-Cell Systems,” Int. J. Hydrogen Energy, 30(9), 973-979 (2005)) have already been reported. Additionally, work coupling fuel reforming with hydrogen production has been reported (see, e.g., Wilhite, B. A., S. E. Weiss, J. Y. Ying, M. A. Schmidt and K. F. Jensen, “Demonstration of 23 wt % Ag—Pd Micromembrane Employing 8:1 LaNi0.95CO0.05O3/Al2O3 Catalyst for High-Purity Hydrogen Generation,” Advanced Materials, 18, 1701 (2006); Deshpande, K. T., B. A. Wilhite, M. A. Schmidt and K. F. Jensen, “Integrated Partial Oxidation and Purification Microsystems for Autothermal Production of Hydrogen from Methanol,” presented at 2005 AIChE Annual Meeting, Cincinnati, Ohio, 36a (2005)). Existing mini- or micro-channel configurations typically consist of alternating plates, each such plate generally featuring a one-dimensional array of geometrically similar channels.
In general, current micro-fabrication methods can limit the potential for heat integration and process intensification. Mini- or micro-channel systems detailed in the literature are typically constructed from patterns micro-machined in materials such as, for example, stainless steel, glass, and/or Si-based materials, and typically include multiple parallel channels (e.g., up to a 1×M array) within a single flat plate, as illustrated in FIG. 1 (see, e.g., Commenge, J. M., L. Falk, J. P. Corriou and M. Matlosz, “Optimal Design for Flow Uniformity in Microchannel Reactors,” AIChE Journal, 48(2), 345-358 (2002); Delsman, E. R., M. H. J. M. deCroon, G. J. Kramer, P. D. Cobden, Ch. Hofmann, V. Cominos and J. C. Schouten, “Experiments and Modeling of an Integrated Preferential Oxidation-Heat Exchanger Microdevice,” Chem. Eng. J., 101(1-3), 123-131 (2004)). In accordance with such methods, heat transport between separate process flows tends to take place along a single direction between the respective channels of vertically adjacent plates arranged in a stack. In addition, one-dimensional analysis demonstrates that the use of high thermal conductivity materials (e.g., silicon, stainless steel) in such applications can significantly limit the thermal efficiency of the necessary heat exchange owing to significant axial conduction losses (see, e.g., Stief, T., O.-U. Langer and K. Schubert, “Numerical Investigations of Optimal Heat Conductivity in Micro Heat Exchangers,” Chem. Eng. Technol., 21(4), 297-303 (1999); Peterson, R. B., “Numerical Modeling of Conduction Effects in Microscale Counterflow Heat Exchangers,” Microscale Thermophysical Engineering, 3, 17-30 (1999)).
Referring now to FIG. 2, current methods for manufacturing mini- or micro-channel networks typically includes methods that employ concurrent micromachining of both distributors and mini- or micro-channels. Individual flat plates are machined with patterns to create rows of mini- or micro-channels addressed by a cross-sectional slice of the distributor. Stacking and sealing of individual plates allows creation of large, two-dimensional arrays of mini- or micro-channels, addressed by simple fluid distributors. Multiple process flows can be distributed amongst the mini- or micro-channels of the array in alternating planes, creating simple distribution patterns. The cost of system scale-up is typically linear, as more plates are required for more channels to accommodate more or different process flows. As practical experience dictates that stacking of more than ten (10) plates is impractical, such systems typically manifest a limited scale.
As such, micro-chemical systems have typically been limited to alternating plate designs manifesting one-dimensional radial distribution patterns of fluidic flow. In addition, the industrial applicability of such systems is further limited by the low mechanical strength and high cost of micromachining individual porous membrane supports.
Thus, despite efforts to date, a need remains for enhanced reactor designs, reactor systems, and associated methodologies. These and other inefficiencies and opportunities for improvement are addressed and/or overcome by the systems and methods of the present disclosure.